I already reported this bug some time ago.
https://forums.ageofempires.com/t/improved-military-production-bug-mongols/225971/3
On a side note you also misread the tooltip. There is no 43% anywhere. 33% increased speed indeed for normal tech which is equivalent to 25% reduced production time. The improved version is intended to give 35% production time reduction which is equivalent to 53.8% increased production speed not 43%. (The normal tech’s tooltip describes the buff as a production speed while the improved version talks about reduction of productio time)
Nevertheless the bug is indeed there and the way the improved tech is researched has an effect on the outcome and you can check the thread linked above for more details (including tooltip vs actual time)